Compositions comprising 5′-ribonucleotides are known for their flavour enhancing properties. They are capable of enhancing the savoury and delicious taste in certain types of food. This phenomenon is described as ‘mouthfeel’ or umami.
The 5′-ribonucleotides are derived from RNA, usually from microorganisms such as yeast. WO2005067734 discloses a process to produce a composition comprising 5′-ribonucleotides where the process comprises subjecting a microorganism to autolysis under conditions at which a substantial part of the RNA remains in a form degradable into 5′-ribonucleotides, then subjecting the autolysate to solid/liquid separation and recovering the RNA-containing cell wall fraction and finally converting the RNA in the recovered RNA-containing cell wall fraction into 5′-ribonucleotides.
Autolytic extracts of microorganisms such as autolytic yeast extracts are concentrates of the soluble materials obtained from the microorganism (e.g. the yeast) after disruption of the cells and digestion (lysis) of the polymeric material (protein, carbohydrates, lipids, nucleic acids). The active microbial (e.g. yeast) enzymes released in the medium after cell disruption contribute to the lysis. These types of extracts are rich in amino acids and generally do not comprise 5′-ribonucleotides because during the autolytic process the native RNA is decomposed or modified in a form which is not degradable into 5′-ribonucleotides. In particular autolytic yeast extracts are used in the food industry as basic taste providers. The amino acids present in the yeast extract add a bouillon-type, brothy taste to the food.
Hydrolytic extracts of microorganisms, on the other hand, are concentrates of the soluble materials obtained after disruption of the cells, digestion (lysis) and addition of proteases and/or peptidases and especially nucleases to the suspension of the microorganism during lysis. The native microbial enzymes are inactivated prior to the lysis. During this process, 5′-ribonucleotides of guanine (5′-guanine mono phosphate; 5′-GMP), uracil (5′-uracil mono phosphate; 5′-UMP), cytosine (5′-cytosine mono phosphate; 5′-CMP) and adenine (5′-adenine mono phosphate; 5′-AMP) are formed. When adenylic deaminase is added to the mixture, 5′-AMP is transformed into 5′-inosine mono phosphate (5′-IMP).
Hydrolytic yeast extracts obtained by this method are rich in 5′-ribonucleotides, especially rich in 5′-GMP and 5′-IMP. Often yeast extracts are also rich in mono sodium glutamate (MSG). 5′-IMP, 5′-GMP and MSG are known for their flavour enhancing properties. They are capable of enhancing the savoury and delicious taste in certain types of food. This phenomenon is described as ‘mouthfeel’ or umami. Yeast extracts rich in 5′-ribonucleotides and, optionally, rich in MSG, are usually added to soups, sauces, marinades and flavour seasonings. Yeast extracts rich in 5′-ribonucleotides are preferably produced using yeast strains with a high RNA content and/or by partial extraction of the cell content.
A problem of the process disclosed in WO2005067734 is that the amount of 5′-ribonucleotides in the composition is too low and that due to the presence of amino acids and short peptides and of others yeast components, they are not very suitable for applications which require cleanliness of taste.
It is an object of the present invention to provide a process to produce compositions rich in 5′-ribonucleotides which are clean in taste, which process is simple and stable, i.e. which yields a constant high level of 5′-ribonucleotides. It is a further object to provide a process to produce yeast extract with little turbidity.